This invention relates to guidewires for facilitating the navigation of medical devices through the vasculature, and in particular to guidewires adapted for passing occlusions in the vasculature.
Navigation of a conventional guidewire involves rotating or applying a torque to the proximal end of the guidewire repeatedly to rotate the distal tip while the wire is pushed. This action is repeated until, by trial and error, the tip enters the desired vessel branch. In navigating guidewires in the vasculature of the body, an important criterion is that the tip of the guidewire be flexible enough to negotiate the sharp turns that are necessary to reach the target area for medical intervention. At the same time, in some medical procedures, particularly in coronary occlusion, flexibility can become a disadvantage when the tip is at the position of a total occlusion. Physicians presently attempt to manipulate the proximal end of the guidewire in a way to punch through such an occlusion. Typically, the flexible guidewire will buckle and fail to provide the passage through the occlusion, which would be necessary in order to implant a stent. Furthermore, after the guidewire has made several bends, the guidewire becomes increasingly difficult to control, requiring repeated attempts to enter a desired vessel branch or gain access through an occlusion. This trial and error method can frustrate the physician and cause additional wall contact and potential trauma.
To address these and other difficulties, magnetically navigable guidewires have been developed which can be controlled with the application of an external magnetic field. An example of magnetically navigable guidewire is disclosed in Werp et al., U.S. Pat. No. 5,931,818 (incorporated in its entirety herein by reference). The user can advance the magnetically navigable guide wire into vessels with little or no contact between the end of the wire and the vessel wall. When the distal end of the guidewire is adjacent the vessel of interest, the user operates a magnetic system to apply a magnetic field (preferably with the aid of a computerized user interface) to deflect the wire tip to align with the vessel side branch. The magnet system can be made sufficiently accurate to direct the distal end of the guidewire into the brach on the first effort, eliminating the trial and error of manually operated guidewires and thereby reducing or eliminating trauma to the vessel wall. The deflection of the guidewire tip is controlled by the external magnets in magnetic navigation, and in normal use, the physician does not need to apply torque to the guidewire. However, while prior magnetically navigable guidewires are very effective at navigating through tortuous paths in the vasculature of a subject, these guidewires do not address the challenge of crossing or pushing through an occluded or partially occluded vessel in the vasculature of a subject's body.